Hitherto, in a process of producing semiconductor parts, for making surface of wafer clean, i.e. without adhesive organic impurities, micro particles and metallic impurities, there are employed a cleaning method and device in which there is used a sulfuric acid-hydrogen peroxide mixture of sulfuric acid and hydrogen peroxide, an ammonia-hydrogen peroxide mixture of aqueous ammonia and hydrogen peroxide, a hydrochloric acid-hydrogen peroxide mixture of hydrochloric acid (HCl) and hydrogen peroxide (H.sub.2 O.sub.2) and pure water (H.sub.2 O), or ultrapure water.
Among them, the cleaning method with the hydrochloric acid-hydrogen peroxide mixture is important because metallic impurities such as Al, Fe, Ni, Cr and Cu can be removed, which may cause problems in performances of semiconductor devices such as leakage at junction, threshold voltage, thickness change of oxide film, breakdown of insulating film.
In the above method, though such metallic impurities can be removed, there is a problem that hydrogen peroxide is decomposed to generate bubbles of oxygen and the oxygen bubbles accelerate adhesion of micro particles such as silicon oxide, silicon, metal oxide and organic materials onto a wafer, which results in that a yield of desired device is lowered and, further, reliability of the device is lowered.
The reason why the particles adhere onto the wafer is not apparent but regarded in the followings.
In case of hydrophilic (lyophilic) particles such as silicon oxide, a flow of the hydrochloric acid-hydrogen peroxide mixture becomes turbulent flow due to the difference between a velocity of rising bubbles and a flow velocity of the hydrochloric acid-hydrogen peroxide mixture in which particles are dispersed, and thus when colliding the particles with a wafer, the vector of velocity of the particle to the wafer is increased as compared as in the state of laminar flow without bubbles.
In case of hydrophobic (lyophobic) particles, the hydrophobic particles let their contact surface area with the hydrochloric acid-hydrogen peroxide mixture decrease to be attracted onto the gas-liquid interface of the mixture. On the other hand, an exposed portion of the silicon wafer without oxide film thereon is hydrophobic (lyophobic) and also lets its contact surface area with the hydrochloric acid-hydrogen peroxide mixture decrease to adsorb the bubbles thereon. As a result, the bubbles stay on the exposed surface portion of wafer, and the hydrophobic micro particles are easy to move from the surface of bubbles and adhere onto the exposed wafer surface which is more stable in surface energy.
Then, in JP-A-775510/ 1988, for example, there is disclosed a cleaning method by using the cleaning device as shown in a diagrammatical view of FIG. 1. In FIG. 1, numeral 1 designates a cleaning bath to clean a member to be cleaned such as wafer and the bath contains the hydrochloric acid-hydrogen peroxide mixture. Numeral 2 designates an outside bath into which the hydrochloric acid-hydrogen peroxide mixture is overflowed from the cleaning bath 1, and numeral 3 designates a piping for circulating and supplying the hydrochloric acid-hydrogen peroxide mixture. Numeral 4 designates a pump for circulating the hydrochloric acid-hydrogen peroxide mixture and numeral 5 designates a filter for removing the particles contained in the hydrochloric acid-hydrogen peroxide mixture. Numeral 7 designates a supplying port and numeral 8 designates a discharging port. The hydrochloric acid-hydrogen peroxide mixture in the outside bath 2 is cleaned by the filter 5 and returned into the cleaning bath 1.
According to the technical method described in the above-mentioned publication, means 6 for trapping bubbles is provided between the filter 5 and a supplying port 7 to decrease an amount of bubbles which come into the cleaning bath 1.
By the method, however, the generation of oxygen due to decomposition of hydrogen peroxide cannot be sufficiently inhibited and the adhesion of micro particles onto the exposed surface portion of wafer cannot be prevented.
Then, an object of the present invention is to provide a cleaning method in which the adhesion of micro particles onto a member to be cleaned can be prevented by decreasing an amount of generation of bubbles.